1. Field of the Invention
The present invention relates to probe arrays used in the fields of chemistry and biochemistry, and methods of manufacturing the probe arrays, and in particular to improvement in the certainty of detection in fluorescence observation.
2. Description of the Related Art
Deoxyribonucleic-acid (DNA) chips have been attracting attention as tools for genetic diagnosis where a plurality of items are examined simultaneously, for example, where the amounts of expressions of different messenger ribonucleic acids (mRNAs) are examined simultaneously, and where different single-nucleotide polymorphisms (SNPs) are examined simultaneously. DNA chips, also called DNA microarrays, are each a probe array in which different kinds of probes, which are known DNA molecules that hybridize with target DNA molecules and RNA molecules, are carried by a plurality of periodically arranged probe carriers.
Antigen chips and antibody chips have also been attracting attention as tools for simultaneously examining the presences of different kinds of antigens and antibodies. Antigen chips are each a probe array in which different kinds of probes, which are known antigen molecules that bond to target antibody molecules, are carried by a plurality of periodically arranged probe carriers. Antibody chips are each a probe array in which different kinds of probes, which are known antibody molecules that bond to target antigen molecules, are carried by a plurality of periodically arranged probe carriers.
One of typical methods of detecting target molecules by using such probe arrays is fluorescence observation (refer to the following for example: Sekine, Mitsuo. Atarashii DNA Chippu no Kagaku to Oyo (Science and Application of New DNA Chips); edited by Kodansha Scientific; published by Kodansha: Jul. 30, 2007; pp. 008-009). In fluorescence observation, a sample solution is first chemically processed so that target molecules are fluorescently modified. The fluorescently modified sample solution is applied to probe carriers of a probe array. Subsequently, while excitation light is applied to the sample solution, fluorescence emitted from the sample solution is observed so as to detect to which probes on the probe array the target molecules have bonded.
The probe array used in fluorescence observation is desired to be quantitative in terms of density of target molecules, regardless of whether the density of target molecules contained in the sample solution is high or low. That is, the probe array is desired to have a wide dynamic range for density of target molecules.
In the known art, however, when the density of target molecules applied to a probe array having a low sensitivity is too low, the presence of the target molecules cannot be detected because the fluorescence emitted from the probe array is too weak. Whereas, when the density of target molecules applied to a probe array having a high sensitivity is too high, the intensity of fluorescence emitted from the probe array becomes saturated, resulting in lack of quantitativeness. In this respect, there is a demand for a probe array having a wide dynamic range and being quantitative regardless of whether the density of target molecules is low or high.
To realize a wide dynamic range with a known probe array, fluorescence observation is in general performed for a plurality of times with various intensities of excitation light. In such a method, however, the need of performing a plurality of observations makes the detection operation complicated. Moreover, after repeated applications of excitation light, fluorescence with which target molecules are modified may diminish, resulting in poor or unstable sensitivity.
To avoid such a problem, there is a demand for a probe array with which a detection result based on a wide dynamic range can be obtained in a single fluorescence observation.